1. Field of the Present Invention
The present invention relates to a variable reluctance device which can e.g., be applied in a stage apparatus or a lithographic apparatus and a method for manufacturing a device.
2. Background Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., including part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. In order to accurately position the patterning device relative to the wafer or substrate, a lithographic apparatus is often provided with one or more positioning device for positioning an object table e.g., holding a patterning device or a substrate. Such positioning devices can e.g., comprise one or more linear motors and/or linear devices such as Lorentz devices for positioning an object table or support. In a lithographic apparatus, both accurate positioning and throughput (e.g., expressed as the number of wafers that can be processed per hour) can be considered equally important. In order to obtain a high throughput, powerful devices and motors are required enabling high accelerations and decelerations of the object table thereby reducing any idle time between consecutive exposures. In order to obtain an accurate positioning, an accurate control of the force as generated by the linear motor or device, is required. In order to meet these requirements, Lorentz devices are often applied for an accurate (e.g., 6 degrees of freedom (DOF)) positioning as such devices enable an accurate control of the generated force. However, compared to other types of devices such as variable reluctance devices, the force density or force vs. dissipation obtainable using a Lorentz device is comparatively small. Compared to Lorentz devices, a variable reluctance device would enable a improved force density while at the same time reducing (moving) mass of the device and the dissipation level. Variable reluctance devices however suffer from the drawback that an accurate force control is rendered difficult because the device force is strongly dependent on the relative position of the magnetic members of a variable reluctance device. As such, using known variable reluctance devices, it is difficult to predict the devices response when a certain magnetizing current is applied.